GBT21A-377

Is circumgalactic HI ubiquitous? A deep search around 4 nearby galaxies

Abstract

We propose to obtain 24 deep GBT spectra, 6 for each of the 4 nearby edge-on star-forming galaxies, stepping along their minor axes out to ~100kpc in the halo.
Absorption-line work suggests this gas surrounds all massive star-forming galaxies and has N(H)~10^19 cm^-2 with a ~1% neutral fraction for N(HI)~10^17 cm^-2. If present in this quantity, this cool (T<10^5K) circumgalactic medium plays a major role in the universal baryon budget. Detecting/setting limits on it in 21-cm emission will provide an important constraint that is complementary to optical, UV and X-Ray spectroscopy. The GBT is the ideal telescope for such an experiment, which relies on surface brightness sensitivity and takes advantage of the unblocked aperture.
In Das et al. (2020), we obtained deep GBT spectra out to ~100 kpc along the minor axes of 2 nearby edge-on star-forming galaxies (NGC891,NGC4565). It resulted S/N>5 detection at each pointing. We compared those GBT spectra with deep interferometer maps from WSRT and found strong evidence for diffuse 21-cm emission. By targeting the next 4 natural (nearby, edge-on) targets: UGC2082, UGC4278, NGC5023, NGC5229, all of which have sensitive WSRT maps, we propose to build the sample size up to test the ubiquity of circumgalactic HI.

Investigators

Name	Institution
Sanskriti Das *	Stanford University
Amy Sardone	Ohio State University; West Virginia University
Nickolas Pingel	Wisconsin at Madison, University of; Indiana University; Australian National University
Souradip Bhattacharyya	Ohio State University
Ness Mayker	Ohio State University
Anthony Machado	Ohio State University; Connecticut, University of
D.J. Pisano	Cape Town, University of
George Heald	Commonwealth Scientific and Industrial Research Organisation
Adam Leroy	National Radio Astronomy Observatory; Ohio State University
Smita Mathur	Ohio State University

* indicates the PI